17,246 research outputs found
On the appearance of translucent edges
Edges in images of translucent objects are very different from edges in images of opaque objects. The physical causes for these differences are hard to characterize analytically and are not well understood. This paper considers one class of translucency edges - those caused by a discontinuity in surface orientation - and describes the physical causes of their appearance. We simulate thousands of translucency edge profiles using many different scattering material parameters, and we explain the resulting variety of edge patterns by qualitatively analyzing light transport. We also discuss the existence of shape and material metamers, or combinations of distinct shape or material parameters that generate the same edge profile. This knowledge is relevant to visual inference tasks that involve translucent objects, such as shape or material estimation.National Science Foundation (U.S.) (IIS 1161564)National Science Foundation (U.S.) (IIS 1012454)National Science Foundation (U.S.) (IIS 1212928)National Science Foundation (U.S.) (IIS 1011919)National Institutes of Health (U.S.) (R01- EY019262-02)National Institutes of Health (U.S.) (R21-EY019741-02
Integrating photovoltaic cells into decorative architectural glass using traditonal glasspainting techniques and fluorescent dyes
Photovoltaic cells can be integrated into decorative glass, providing a showcase for this renewable technology,
whilst assisting in the creation of sustainable architecture through generation of electricity from the building surface. However, traditional, opaque, square, crystalline-silicon solar cells contrast strongly with their
surroundings when incorporated into translucent, coloured glazing. Methods of blending photovoltaic cells into
their surroundings were developed, using traditional glass painting techniques. A design was created in which
opaque paint was applied to the areas of glass around underlying photovoltaic cells. Translucent, platinum paint
was used on the glass behind the photovoltaic cells. This covered the grey cell backs whilst reflecting light and
movement. The platinum paint was shown to cause a slight increase in power produced by photovoltaic cells
placed above it. To add colour, very small amounts of Lumogen F dye (BASF) were incorporated into a silicone
encapsulant (Dow Corning, Sylgard 184), which was then used hold photovoltaic cells in place between sheets of
painted glass. Lumogen dyes selectively absorb and emit light, giving a good balance between colour addition
and electricity production from underlying photovoltaic cells. When making sufficient quantities of dyed
encapsulant for a 600 x 450 mm test piece, the brightness of the dye colours faded, and fluorescence decreased,
although some colour was retained. Improvement of the method, including testing of alternative encapsulant
materials, is required, to ensure that the dyes continue to fluoresce within the encapsulant. In contrast, the
methods of adding opacity variation to glass, through use of glass painting, are straightforward to develop for use
in a wide variety of photovoltaic installations. Improvement of these methods opens up a wide variety of
architectural glass design opportunities with integrated photovoltaics, providing an example of one new medium
to make eco-architecture more aesthetically pleasing, whilst generating electricity
Preliminary results of accelerated exposure testing of solar cell system components
Plastic samples and solar cell sub modules were exposed to an accelerated outdoor environment in Arizona and an accelerated simulated environment in a cyclic ultraviolet exposure tester which included humidity exposure. These tests were for preliminary screening of materials suitable for use in the manufacture of solar cell modules which are to have a 20-year lifetime. The samples were exposed for various times up to six months, equivalent to a real time exposure of four years. Suitable materials were found to be FEP-A, FEP-C, PFA, acrylic, silicone compounds and adhesives and possibly parylene. The method of packaging the sub modules was also found to be important to their performance
Redefining A in RGBA: Towards a Standard for Graphical 3D Printing
Advances in multimaterial 3D printing have the potential to reproduce various
visual appearance attributes of an object in addition to its shape. Since many
existing 3D file formats encode color and translucency by RGBA textures mapped
to 3D shapes, RGBA information is particularly important for practical
applications. In contrast to color (encoded by RGB), which is specified by the
object's reflectance, selected viewing conditions and a standard observer,
translucency (encoded by A) is neither linked to any measurable physical nor
perceptual quantity. Thus, reproducing translucency encoded by A is open for
interpretation.
In this paper, we propose a rigorous definition for A suitable for use in
graphical 3D printing, which is independent of the 3D printing hardware and
software, and which links both optical material properties and perceptual
uniformity for human observers. By deriving our definition from the absorption
and scattering coefficients of virtual homogeneous reference materials with an
isotropic phase function, we achieve two important properties. First, a simple
adjustment of A is possible, which preserves the translucency appearance if an
object is re-scaled for printing. Second, determining the value of A for a real
(potentially non-homogeneous) material, can be achieved by minimizing a
distance function between light transport measurements of this material and
simulated measurements of the reference materials. Such measurements can be
conducted by commercial spectrophotometers used in graphic arts.
Finally, we conduct visual experiments employing the method of constant
stimuli, and derive from them an embedding of A into a nearly perceptually
uniform scale of translucency for the reference materials.Comment: 20 pages (incl. appendices), 20 figures. Version with higher quality
images: https://cloud-ext.igd.fraunhofer.de/s/pAMH67XjstaNcrF (main article)
and https://cloud-ext.igd.fraunhofer.de/s/4rR5bH3FMfNsS5q (appendix).
Supplemental material including code:
https://cloud-ext.igd.fraunhofer.de/s/9BrZaj5Uh5d0cOU/downloa
The identification of cloud types in LANDSAT MSS images
The author has identified the following significant results. Five general families of clouds were identified: cumulonimbiform, cumuliform, stratiform, stratocumuliform, and cirriform. Four members of this five-fold primary division of clouds were further divided into a number of subgroups. The MSS observed and recorded earth radiation in four different wavebands. Two of these bands (4 and 5) image in the visible portion of the electromagnetic spectrum, while the others (6 and 7) image the short wave portion, or just into the infrared. The main differences between the appearances of clouds in the four wavebands are related to the background brightness of land and sea surfaces
Intermittency of interstellar turbulence: extreme velocity-shears and CO emission on milliparsec scale
The condensation of diffuse gas into molecular clouds occurs at a rate driven
largely by turbulent dissipation. This process still has to be caught in action
and characterized. A mosaic of 13 fields was observed in the CO(1-0) line with
the IRAM-PdB interferometer in the translucent environment of two low-mass
dense cores. The large size of the mosaic compared to the resolution (4 arcsec)
is unprecedented in the study of the small-scale structure of diffuse molecular
gas. Eight weak and elongated structures of thicknesses as small as 3 mpc (600
AU) and lengths up to 70mpc are found. These are not filaments because once
merged with short-spacing data, they appear as the sharp edges of larger-scale
structures. Six out of eight form quasi-parallel pairs at different velocities
and different position angles. This cannot be the result of chance alignment.
The velocity-shears estimated for the three pairs include the highest ever
measured far from star forming regions (780 km/s/pc). Because the large scale
structures have sharp edges, with little or no overlap, they have to be thin
CO-layers. Their edges mark a sharp transition between a CO-rich component and
a gas undetected in the CO line because of its low CO abundance, presumably the
cold neutral medium. We propose that these sharp edges are the first
directly-detected manifestations of the intermittency of interstellar
turbulence. The large velocity-shears reveal an intense straining field,
responsible for a local dissipation rate several orders of magnitude above
average, possibly at the origin of the thin CO-layers.Comment: 16 pages, 11 figures, Accepted for publication in Astronomy and
Astrophysic
Bandwidth-resonant Floquet states in honeycomb optical lattices
We investigate, within Floquet theory, topological phases in the
out-of-equilibrium system that consists of fermions in a circularly shaken
honeycomb optical lattice. We concentrate on the intermediate regime, in which
the shaking frequency is of the same order of magnitude as the band width, such
that adjacent Floquet bands start to overlap, creating a hierarchy of band
inversions. It is shown that two-phonon resonances provide a topological phase
that can be described within the Bernevig-Hughes-Zhang model of HgTe quantum
wells. This allows for an understanding of out-of-equilibrium topological
phases in terms of simple band inversions, similar to equilibrium systems
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